It gave us the first ever eradication of an infectious disease; now it may help defeat cancer. Smallpox vaccine has doubled the survival time of people with advanced liver cancer.
The vaccine that eradicated smallpox consists of a live virus, Vaccinia, with a surprising taste for tumours. It prefers to infect cancer cells because they turn off the antiviral protein interferon and turn on signalling molecules that attract Vaccinia. Early experiments in a variety of tumours reported in 2007 suggested that this might make the virus, which has been used safely in millions of people, a revolutionary cancer treatment.
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